Welltech ATA172plus not sending/receiving faxes

Ok, so I've tried everything to get this to send/receive faxes correctly and I'm out of ideas. I setup the Welltech ATA172plus via 3CX link, but for some reason I can't send or receive faxes. Our fax machine will dial and connect, but it never gets pass that point, same with receiving faxes. It just connects (some fax noises) for a few seconds and then disconnects. No data is sent or received. Anyone got an idea whats happening?

To start with, FoIP is a difficult process regardless, as its success is largely dependent on the reliability and stability of your Internet provider to deliver a consistent stream of data. t.38 is a protocol that attempts to overcome some of the issues associated to the carriage, but it can only do so much. The g711 fall back is more of a "Hail Mary" play, but does have its place when t.38 is not supported. If the provider supports t.38 and the fax is not successful, then it is not likely that g711 will save the day.

The fax machine may also play a part.You might try to see if you can lower the speed of the fax to - 9600, 4800 or 2400. You may also need to try with fax error correction off and on. HP has an automated fax test number that you can Google and use to send a test fax. If the fax is received by them successfully, they will send a fax back using the observed CID.

I think I have tried virtually every ATA known to man - Patton, Welltech, Cisco, Planet, Grandstream, Net-Gen Communications and more...both using 3CX as well as stand-alone with registrations direct to the provider. I have come to the following conclusions -
1. t.38 is a standard and all profess to have t.38 support
2. None are foolproof and while some may seem to have varying degrees of success, I cannot state that one was categorically better than another. I tested each in a lab using ideal conditions and all performed equally well.
3. What mattered was the field conditions and the stream of data that was able to be delivered at the front-end. It was here that some appeared to be somewhat more tolerant than others, but I cannot attest to the conditions being the same at the time that each was being tested. I tested several model at the same location on the same day, but again, could there have been differences, yes.
4. I had some ATA;s that had been installed and working over time, but then for some reason issues would arise and I would have to go out and then tinker with settings on speeds, QoS, audio gain and the like in the hopes that I could hit the right combination.
5. I found that some fax machines, for whatever reason, are not a friendly as others. Sharp All in Ones was one brand that gave me fits,.
6. I decided that the amount of time and effort spent on FoIP using analog ATAs was far more of maintenance issue than I was willing to undertake and clients were not satisfied with the consistency compared to their prior experience using POTS.
7. I now only use HTTPS fax devices or provider delivered POTS (copper or cable) and avoid analog ATA FoIP like the plague.
8. I still have a couple using ATAs with great success, but the common factor is that they have fiber Internet carriage. Unfortunately, in my area, that it is not very prevalent and also quite expensive.

A wireshark capture may show what is going on, but if the carriage is not up to snuff, then nothing will help.Those providers that indicate support for t.38 do so as a pass-thru. This means that if they detect t.38, they will send the Invite to the far end requesting t,38 and if the Invite is successful they will simply allow the stream to pass thru their network unaltered, If there is an issue, they may try and re-Invite to g711u, Most providers supporting t.38 indicate that while their networks support it, that given the nature of FoIP, they are not in a position to troubleshoot it.

Sorry for the long rant, but there are a number of posts on the forum citing fax issues and I get the feeling that many think that it should be simple to implement. 3CX has made it more so with the addition of g711 fallback, but they do not control anything the second the carriage leaves the system NIC card.